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Java / Java 21 Collection Framework features Interview questions

How can you optimize a producer-consumer pattern using ArrayDeque's sequenced methods?

ArrayDeque already supported first/last operations before Java 21, so what changes is mainly that this same producer-consumer pattern can now be written against the general SequencedCollection interface, making the code reusable across other sequenced types too.

SequencedCollection<Task> queue = new ArrayDeque<>();
// producer
queue.addLast(new Task("build"));
// consumer
if (!queue.isEmpty()) {
    Task next = queue.removeFirst();
    process(next);
}

Because ArrayDeque is backed by a resizable circular array rather than a linked structure, both addLast() and removeFirst() run in amortized O(1) time with better cache locality than a linked-node-based LinkedList, which makes it a strong default choice for this pattern.

Declaring the variable's type as SequencedCollection<Task> instead of the concrete ArrayDeque<Task> also means you could later swap in another sequenced implementation without touching the producer/consumer logic itself.

ArrayDeque is backed internally by:
Declaring the queue variable as SequencedCollection instead of ArrayDeque mainly gains:

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